The overall goal of this proposal is directed at understanding virus and receptor interactions. Three- dimensional structures will be determined of small non-enveloped viruses interacting with cellular components that modulate the viral life cycle during cell recognition, entry or viral uncoating. Recognition of specific cellular receptors is a significant part of the determination of host range and tissue tropism. Viruses have evolved to use a large variety of cell-surface molecules as receptors with some viruses using commonly found chemical groups whereas other viruses recognize very specific molecules. Hence, the distribution of the receptor will determine the tropism of the virus and the symptoms of the infection. For the research proposed here, two different viral systems will be used: positive stranded ssRNA picornaviruses, including echovirus 7 and coxsackieB3; also the ssDNA-containing parvoviruses, including family members feline panleukopenia virus and canine parvovirus. Both families of viruses are simple, non-enveloped, icosahedral viruses with an external diameter of approximately 300 Angstroms.